Add an operation for creating book reviews

Your model now has two entities, so the next step is a way to add new book review entries. You do this with an operation that creates a book review.

Add the following Rell code to src/main/operations.rell:

operation create_book_review(isbn: text, reviewer_name: text, review: text, rating: integer) {  val book = book @ { .isbn == isbn };  create book_review (    book,    reviewer_name,    review,    rating  );}

The structure mirrors the create_book operation, with one difference: it links the review to a book. Books are keyed by isbn, so that value identifies which book the review belongs to.

Inside the operation

When you submit the create-review operation to a Chromia node, the node produces a new transaction and stores the data in the dapp table state. The flow looks like this:

• A user signs the transaction create_book_review("ISBN1234", "Alice", "It was a great book!", 5).
• The Chromia Node receives the transaction, validates it, and passes it on to the blockchain.
• Inside the operation:

  val book = book @ { .isbn == isbn };  create book_review (    book,    reviewer_name,    review,    rating  );

The operation looks up the book in the dapp table state and inserts a new book_review row that references that book.

• Once the transaction is confirmed, it goes into a block on the blockchain and the dapp table state reflects the change.

Adding unit tests

Next, write a test that confirms the book review operation behaves correctly. Rell supports test modules, which make writing tests simple.

In src/test/book_review_test.rell, extend the imports so they include book_review and create_book_review:

import main.{ book, create_book, get_all_books, book_review, create_book_review };

Then add this test code to the same file:

function test_add_book_review() {    rell.test.tx()        .op(create_book("123", "Book1", "Author1"))        .op(create_book_review("123", "Reviewer1", "ReviewText1", 5))        .op(create_book_review("123", "Reviewer2", "ReviewText2", 3))        .run();    val reviews = book_review @* { };    val book = book @ { .isbn == "123" };    assert_equals(reviews.size(), 2);    assert_equals(book, reviews[0].book);    assert_equals(reviews[0].reviewer_name, "Reviewer1");    assert_equals(reviews[0].review, "ReviewText1");    assert_equals(reviews[0].rating, 5);}

The test runs a single transaction containing three operations: one creates a book, and the other two create reviews linked to that book.

• assert_equals(reviews.size(), 2); confirms that exactly two entries exist.
• assert_equals(book, reviews[0].book); confirms that the review points to the right book.
• assert_equals(reviews[0].reviewer_name, "Reviewer1") checks the reviewer's name.
• assert_equals(reviews[0].review, "ReviewText1") checks the review text.
• assert_equals(reviews[0].rating, 5) checks the rating.

Run the tests with this command:

chr test

The output should report that every test passed:

TEST RESULTS:OK test.book_review_test:test_add_bookOK test.book_review_test:test_get_booksOK test.book_review_test:test_add_book_reviewSUMMARY: 0 FAILED / 3 PASSED / 3 TOTAL***** OK *****

Testing with a local Chromia node

To try the new operation against a local Chromia node:

1. Update or start the local Chromia node:

   • If your node is already running, update it with:

     chr node update

   • If your node is not running, start it with:

     chr node start

   Note: Changes from chr node update can take a short time to apply. You may have to wait until the next block is processed before the query is available.

2. Submit a transaction that adds a book review:

   Run this command to create the transaction:

   chr tx --await create_book_review "ISBN1234" "Alice" "It was a great book" 5

   You should see:

   transaction with rid TxRid(rid=<RID>) was posted CONFIRMED

This output means the transaction is on the blockchain and the state now holds a row containing your book review.